Increase code coverage

[edeandrea]

We'd like to have more tests to increase our code coverage. Also more tests around other use cases as well (other parts of the APIs).

[lemosdevv]

hello, I would like to help

[edeandrea]

Thanks @lemosdevv !

There are lots of gaps currently in https://github.com/docling-project/docling-java/blob/main/docling-serve/docling-serve-client/src/test/java/ai/docling/serve/client/AbstractDoclingServeClientTests.java

We should be testing all the various options that are available in the api but unfortunately we aren't right now. Just simple cases.